When adding a .zip file it always says invaild zip even tho it's vaild. Is there any fix to this?

This looks like an issue within butler itself, so unfortunately I can't help debug it much. Some things you could try:

• unzip + rezip the files and try uploading again
• rezip the files from the original folder and try uploading again
• rezip the files using a different archive tool (windows has a built-in one, but you could try a third party one like 7zip)

If the issue persists, you'll probably have more luck reporting it via itch support or their github issues.